Platinum is a precious metal for which there are many uses, both industrial and non-industrial. Many of these applications take the form of platinum plating, where platinum is plated on a metal surface or substrate. For example, the automotive industry uses platinum plating in the production of catalytic converters. Platinum plating is also used to coat medical instruments and devices, such as catheters or electrical contacts on medical devices and surgical instruments. Platinum is also used in the electronics and electrical industries for electrical contacts. Platinum coated electrodes are also used in the processes for refining oil and manufacturing fertilizers and explosives. As a final example, platinum is used in the jewelry industry to plate less expensive metals. Platinum has a high luster and is resistant to tarnishing and oxidation. Further, platinum resists oxidation and does not oxidize at high temperatures such as those encountered in hot exhaust gases from combustion engines and the like. Platinum is also hypoallergenic.
However, platinum is very expensive. Therefore, any plating process preferably will minimize the waste of platinum. For example, it is preferable that a plating process deposit platinum only on the target surface and not on other surfaces. The deposition of platinum onto a container holding the plating solution, onto jigs or fixtures holding the object to be plated (e.g., a workpiece), or onto electrodes or other equipment used in the plating process, is wasted platinum. It is also preferable that platinum be deposited to the minimum desired thickness. Overplating results in a platinum plating that is thicker than required, which means that more platinum was used in the plating process as compared to a thinner but still adequate plating. Overplating and wasted platinum not only require more platinum to be used than is necessary, but are also reflected in the cost of the article(s) being plated. Ideally, only the minimal amount of platinum needed would be used for plating articles, thereby reducing platinum costs and the platinum related costs of the article(s) being plated.
There are two conventional approaches to platinum plating: electroplating and electroless plating. In electroplating, two electrodes are immersed in a solution of electrolyte containing platinum ions. The voltage difference between and anode and cathode creates an electric field (e.g., an electrical current) in the solution, which facilitates the plating of a film of platinum onto the object. The object being plated may serve as one of the electrodes, for example. However, electroplating suffers from several drawbacks. One drawback is that the process is directional. Therefore, it is more difficult to evenly plate irregularly shaped objects. Depending on the physical setup, the platinum may also coat the electrodes or fixtures, resulting in more waste.
In contrast, electroless plating does not use electrodes but uses a reducing agent to facilitate a chemical reaction for plating a metal substrate. Typically, the metal substrate to be plated is submerged in an electroless plating solution that contains both platinum ions and a reducing agent. The platinum ions are reduced to elemental platinum that plates onto the metal substrate. Electroless plating also has disadvantages, some due to the use of the reducing agent. For example, the reducing agent is active regardless of whether a metal substrate is submerged in the plating solution, because platinum is always present in the solution. Thus, the chemical reaction in the electroless plating solution continues even if no metal substrate is present. The solution will consume itself or “plate out”, requiring the replenishment of more chemicals and platinum and driving up the cost. Not only does electroless platinum plating drive up the cost, more importantly, the “plating out” of the bath means once the platinum is totally consumed, one cannot plate any more. The bath is basically dead. Bath stability is another issue that affects the cost and efficiency of electroless plating. As the bath decomposes, expensive platinum is wasted and the bath and associated tools covered by the bath are contaminated with platinum residue. The platinum residue is difficult to remove.
There are continuing efforts to improve platinum plating technology.
Although the above-described drawings depict various examples of the invention, the invention is not limited by the depicted examples. It is to be understood that the drawings are not necessarily to scale.